This invention relates to a method of non-destructive inspection of concrete conduits and cylinders, such as for example water pipes and water reservoir vessels, which are reinforced with metal wires. The invention also relates to apparatus for carrying out such inspections.
There are many wire-reinforced concrete structures in use to contain or to conduct pressurized fluids, for example forming conduits in piping systems for water or forming water reservoir vessels. Typical concrete conduits are formed of concrete pressure pipe. Concrete pressure pipe consists of a thin steel cylinder, over which a layer of concrete is cast. Metal reinforcing wires are wound helically, either directly onto the metal cylinder or onto a layer of concrete cast on the cylinder. Often, a second layer of concrete is cast over the metal reinforcing wires. The exterior of the pipe is then finished with a layer of mortar.
Concrete vessels used for water storage (as for example to contain water for distribution) are usually cylindrical in cross-section, although they are occasionally oval in cross-section. The vessel is wrapped around its circumference with wire to provide compressive force to the concrete of the reservoir to support the water contained within the vessel forming the reservoir. Typically, the wire is of circular cross section, although other cross-sections (e.g. rectangular) are known as well.
The purpose of the reinforcing wires is to keep the concrete that they overlie in compression. Over time, the wires may corrode and eventually break. When this happens, it is possible that a rupture of the concrete conduit or reservoir vessel will occur, leading to escape of the pressurized fluid which it contains.
It is very expensive to replace an entire conduit or reservoir vessel. Therefore, it is preferred to carry on some sort of inspection procedure, to determine where wires have broken. This permits remedial work to be carried out only in locations that need it.
Prior techniques of inspection have not been completely successful. Some work has been done with remote eddy field current devices, and U.S. Pat. No. 6,127,823 of Atherton has proposed simultaneously using remote eddy field effects and transformer coupling effects for inspection. However, as admitted in that patent, the interpretation of the test results is complicated. Further, because the device of the Atherton patent preferably has a spacing of two to three pipe diameters between its exciter coil and its detector coil, it is not suited to detecting wire breaks near the ends of the pipeline, i.e. within two to three pipeline diameters of the end.
According to the invention, an inspection device is provided for concrete pipes or vessels having a cylindrical wall reinforced with wires wound around the wall, or concrete vessels having an oval wall with wires wound around the wall. The device has one or more detectors proximal to the wall to be inspected. The detector can be inside or outside the wall. When the inspection device is used for inspecting pipelines, the detector is preferably inside the wall, attached to a vehicle which can be pulled through the pipeline.
In one embodiment, the detector is a coil having an axis parallel to the axis of the pipeline, and with an edge proximal to the wall of the pipeline. In a preferred embodiment, there are two detectors, axially spaced from each other. Preferably, where the detectors are coils, the detector coils have a diameter considerably less than the diameter of the pipeline being examined, and more preferably, not more than one-third of the diameter of the pipe being examined.
In another embodiment, the detector is a non-coil detector of electromagnetic fields, preferably a giant magneto resistive (GMR) sensor. Preferably, the detector comprises three GMR sensors, with their axes of sensitivity to magnetic flux orthogonal to one another. The magnetic flux in the direction desired to be measured (for example, along an axis parallel to the axis of a cylindrical pipeline or vessel) is measured by measuring the flux in the three orthogonal directions represented by the three detectors, and resolving the vectors to determine the flux in the desired direction.
In one manner of operation, the invention provides a driver coil to create an electromagnetic field, which creates a current flow through the wires forming part of the wire-wound concrete pipe or vessel. The voltage and other effects induced by this current in a detector are then measured.
Preferably, the driver coil has its axis orthogonal to the detectors, which may be radial to the pipe or vessel in one manner of orientation of the driver coil in relation to a cylindrical pipe or vessel being inspected. The axis of the driver coil will be discussed with relation to a cylindrical pipe or vessel, which is the normal case. If a pipe or vessel has an oval cross section, the two axes are parallel to one another. In that case, the term xe2x80x9cthe axisxe2x80x9d used herein means either of the parallel axes.
It is preferred that the axis of the driver coil lies in a plane extending across the pipe or vessel, that is transverse to an axis of the pipe, and intersecting the detector. Where there are two detectors, the axis of the driver coil is preferably in a plane at right angles to an axis of the pipe and intermediate the two detectors. This has the advantage that there is no separation along the axis of the pipeline between the detector and the driver. This permits measurements to be taken up to only a few centimetres of the end of the pipe, which is not possible with apparatus where an axial separation must be maintained. Although not preferred, it is possible to use the invention with an axial separation along the pipe between the detector and the driver coil. Distances of up to 3.05 m. (10 feet) separation in a 6.1 m. (20 foot) diameter pipe have been found to work. However, such axial separation has no benefit, requires a longer mount for the equipment, and prevents taking readings near the ends of pipes.
In one embodiment, the detector is offset from the driver coil along an inner surface circumference of the pipe. The detector may be diametrically opposite the pipe from the driver coil. Where the detector is a coil, the axis of the detector coil is preferably parallel to the axis of the pipe. It is possible to have a driver coil that is not completely diametrically opposed to the detector, but it is preferred that the radius along which an axis of driver coil is, should at least be on a side of the central axis of the pipe that is remote from the detector. For large diameter pipes, such as 6.1 m. (20 foot) diameter pipes, it is preferable not to have the driver coil diametrically opposed from the detector, but circumferentially offset from it, to reduce the length of the equipment mounting boom on which the detector and driver coil are mounted.
In one method of operation, the invention provides a driver coil to create an electromagnetic field, which creates a current flow through the wires that wrap a concrete cylinder, such as a water reservoir or a very large diameter pipe. The voltage and other effects induced by this current in a detector located proximal to an exterior surface of the concrete cylinder remote from the driver coil are then measured.
The detector is remote from the driver coil along an outer surface circumference of the concrete cylinder. The detector may be diametrically opposite the cylinder under test from the driver coil. For large diameter cylinders, for example 6.1 m. (20 foot) diameter pipes or water reservoirs of even larger diameter, if the driver coil is not diametrically opposed from the detector, it is circumferentially offset from it. Where the detector is a coil, the axis of the detector coil is parallel to the axis of the cylinder under test.
There can be appreciable interference to the signal produced by the detector through direct magnetic flux coupling between the driver and the detector, for example, the magnetic flux formed within the pipe, between the detector and the driver. To counter this, it is preferable to orient the detector axis to be orthogonal to the driver axis. Further reduction of the direct magnetic flux coupling between the driver and the detector can be obtained by placing a substance of high permeability, which shields magnetic flux, in a position to block or substantially attenuate such magnetic flux. Mu-metal is a metal alloy that is expressly built to prevent passage of magnetic force, so a shield of mu-metal is preferred.
In a particularly preferred embodiment of the invention, a detector device according to the invention is mounted on a vehicle movable through the pipe. The vehicle is provided with a means for determining its location or distance of travel precisely. The vehicle proceeds down the pipe, while logging information from the magnetic pipe inspection and location or distance information. The location determination means provides a precise location, so that the information that is received about the state of the wires can be correlated to a particular location along the pipe. Optionally, the vehicle is also fitted with means to propel it through the pipe, and hydrophone means, which can carry out an acoustic examination of the walls as the vehicle is passing it through.
The vehicle is preferably sized so that, in a large pipeline, it can be placed in the pipeline through inspection ports, which are spaced along the pipeline. The vehicle can also be stopped at such inspection ports for the recharging of batteries and removal of recorded data. If desired, a whole or partial analysis can be done at the vehicle progresses through or traverses the pipe. The results can be displayed graphically to the operator. Alternatively, the data can be removed and analyzed at a remote location.
In one of its aspects, the invention provides an inspection apparatus for detecting discontinuities in spirally wound metallic wires embedded the wall of a concrete pipe, comprising a detector for producing an output responsive to a magnetic flux and a driver means to create magnetic flux and located not more than one pipe diameter along the axis of the pipe from the detector. Preferably, the detector is a coil oriented with an axis parallel to the concrete pipe, and the driver means is a coil with an axis orthogonal to the to the axis of the concrete pipe for inducing a current in the wires. The detector is oriented proximal to a surface of the pipe, preferably an inside surface.
In a preferred embodiment, the inspection apparatus includes displacement sensor means to produce an output representative of at least one distance of the detector a from a known location and means for causing the detector to move along a wall of such pipe as well as means for storing outputs corresponding to the flux detected by the detector and the displacement of the detector from such known location.
In another of its aspects, the invention provides a method of detecting discontinuities in spirally wound metallic wires reinforcing a concrete pipe, comprising providing a driving signal to a driver means having an axis oriented orthogonal to the axis of a concrete pipe and disposed proximal to an inside surface thereof to generate an induced current in said wires and providing a detector for producing an output responsive to a magnetic flux in a direction axial to said pipe, the detector being located in close proximity to an interior wall of a pipe and within one pipe diameter of the driver along the axis of the pipe. In accordance with the method, the detector is moved along the wall of the pipe, and the output and the location of the detector is recorded as it moves.
In another aspect, the invention provides a method of testing the spirally wound metallic wires reinforcing the wall of a concrete pipe, by generating a driving signal with a signal generator, providing a detector located in a fixed position relative to the signal generator and not more than one pipe diameter axially along the pipe therefrom, moving the detector and signal generator along the pipe, detecting a signal with said detector in response to said driving signal and determining the location along the pipe where the detector is located at the time each detected signal is detected. Preferably, the periodic driving signal is generated at more than one frequency, and the detector signal is recorded over a range of locations traversed along a length of pipe.
In another of its aspects, the invention provides a method for testing the spirally wound reinforcing wires embedded in the wall of a concrete pipe along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means disposed proximal to a surface of the pipe, the magnetic flux production means and the magnetic flux detector means in a spaced relationship to the other and axially disposed within one pipe diameter to the other. The magnetic flux production means produces a magnetic field in response to a driving signal and the magnetic flux detector means produces a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means. The method comprises providing a driving signal of at least one frequency; receiving a detector signal; producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the driving signal; and recording the output representative of the detector signal and the location; whereby at least one output is recorded over a range of locations traversed along a length of pipe.